The present invention relates to electronic components and, in particular, to components constructed to thermally match a supporting substrate of a higher level circuit assembly.
The substrates of the components contemplated in the present invention are thermally matched to the substrate of the next higher level circuit assembly to which they are attached. Preferably, the thermal coefficient of expansion (TCE) of the component substrate matches the TCE of the higher level assembly substrate. Component terminations are formed at solder filled electrical junctions. The terminations may be located to reduce thermal stress at the component's connection to a higher level assembly. The terminations may also be partially exposed to permit component testing, once mounted.
Advantages accrue in a thermally dynamic environment due to reduced thermal stress to the thermally matched component at the termination interface. Final form factor flexibility is also provided by sizing the thermally matched component to dimensions required. Absence of leads and lead length afford low electrical inductance and hence higher frequency performance. Side terminations are available for electrical test and visual quality inspection.
Conventional higher level circuit assembly typically requires the separate handling and attachment of many lead frame piece part components to an impregnated resin printed circuit (PC) board. Assembly of these leaded components typically requires the separate fluxing, soldering, cleaning, aligning, molding, deflashing and curing of each part. Prior to assembly, many of these leaded components may also be subject to lead forming, lead cutting, fluxing, tinning, and cleaning. Co-planarity of populated leads is extremely important for reliable solder connections to the circuit board.
Component malfunctions or cracks may arise from thermal mismatches that occur at the point of electrical connection between the substrate of a higher level assembly and components populated about the assembly. Defects of these types arise because the substrate of available discrete, hybrid and integrated circuit components is normally formed from a material exhibiting a widely divergent TCE to that of the supporting substrate of a higher level circuit assembly. For example, the substrate of many integrated circuits and hybrid components are selected from various relatively heat transmissive materials versus the less transmissive material of the PC board, such as resin or polyimide impregnated boards. Over time, the relative differences in thermal expansion and contraction between each component substrate and supporting PC board can lead to a defective connection, cracks in the encapsulant, and malfunction. The potential for such defects increases as the physical size and number of component terminations increases.
The attendant lead frames and bonding conductors of a component can also effect the impedance characteristics of a populated higher level circuit assembly. Desirably, as few components as possible and components having short lead lengths or solder bump terminations are preferred over components having lead frames. Varieties of hybrid and integrated components can be used to this end. The electrical function and circuitry of the latter components can be tailored to the higher level assembly with which it is to be used.
In an exemplary hybrid thermally matched component containing resistors and capacitors, the invention offers simplicity in reduced parts count and reduced processing complexity during subsequent higher level circuit assembly. High frequency performance is enhanced at the higher level assembly with surface mount terminations.
Also disclosed are thermally matched, multi-layered transmission line components and thermally matched and resistive network circuit components.
All hybrid components are constructed to provide an optimal thermal match between each component and a support substrate of the higher level assembly, such as a hybrid ceramic carrier or resin or polyimide impregnated PC board. The invention, however, is adaptable to wide varieties of components.